I performed this update using the newer Pi Zero W, though it should definitely work on the Pi Zero or any other Pi with slight modifications.

I updated blueZ 5.39 to 5.45 which means you no longer MUST compile/run with experimental features enabled (but you can).

The relevant Mono changes have been merged to trunk so you can run Beta builds on the Pi 2/3, but you still have to build from scratch for Pi Zero (and, spoiler alert, building Mono seems to take MUCH longer on the Zero now)

Lastly, and I think this might have been tripping people up, you should run hash -r after installing. I found that bash was caching the location of the old mono installation even after installing my scratch built mono to /usr/local.

I hope this helps some of you that have been having issues. I'm going to go through this again when I get time and try and develop a script or post an image.